2.1.2. MBIST Controller implementation

The L220 MBIST Controller block that Figure 2.7 shows, consists of two major blocks:

Figure 2.7. L220 MBIST Controller block

This section is subdivided into:

MBIST Controller and dispatch unit interface

The MBIST Controller and the dispatch unit communicate using the following signals:

MBISTTX[11:0]

This signal is an output of the MBIST Controller that goes to the dispatch unit. Table 2.10 shows the signals.

Table 2.10. MBISTTX signals

MBISTTX bitDescription
0Reset address
1Increment address
2Access sacrificial row, used during bang patterns
3Invert data/instruction data in
4Checkerboard data
5Write data
6Read data
7Yfast/nXfast
8Direction
9Enable bitmap mode
10Increment go/nogo dataword selection
11Latency stall control

When the instruction shift is enabled, data shifts in on bit 3, normally Invert data and shifts into the instruction scan chain of the dispatch unit. The MBISTTX[11:0] interface is ARM-specific and intended for use only with the L220 MBIST Controller.

MBISTRX[2:0]

This signal is an output of the dispatch unit that goes to the MBIST Controller. The behavior of MBISTRX[2:0] is ARM-specific and is intended for use only with the L220 MBIST Controller. The address expire signal is set when both the row and column address counters expire. Table 2.11 shows the signals.

Table 2.11. MBISTRX signals

MBISTRX bitDescription
0Address/instruction data out/fail data out
1Shadow pipeline empty
2Nonsticky fail flag

L220 MBIST Controller block top level I/O

The top level I/O of the L220 MBIST Controller consists of the L220 interface. See Appendix A Signal Descriptions and the inputs and outputs that Table 2.12 shows.

Table 2.12. L220 MBIST Controller top level I/O

SignalDirectionFunctionValue, MBIST modeValue, function mode
MBISTDATAINInputSerial data inToggle0
MBISTDSHIFTInputData log shiftToggle0
MBISTRESETNInputMBIST resetToggle0[1]
MBISTRESULT[2:0]OutputOutput status busStrobe-
MBISTRUNInputRun MBIST testToggle0
MBISTSHIFTInputInstruction shiftToggle0
MTESTONInputMBIST path enableToggle0
SCANENABLEInputATPG signal00
SCANMODEInputATPG signal00

[1] MBISTRESETN and MTESTON must be LOW in functional mode

Note

nRESET of the L220 Cache Controller must be HIGH in MBIST test mode.

The following signals have additional information:

SCANENABLE

Preservation of array state is required when performing multiload ATPG runs or when performing IDDQ testing. The L220 MBIST Controller keeps all L220 RAM chip select signals LOW with the SCANENABLE signal. After performing MBIST tests to initialize the arrays to a required background, the Automatic Test Pattern Generator (ATPG) test procedures must assert SCANEANABLE during all test setup cycles in addition to load/unload. Any clocking during IDDQ capture cycles must have array chip select signals constrained.

MBISTRESULT[2:0]

During tests, the MBISTRESULT[1] signal indicates failures. You can operate using two modes, by configuring bit 5 of the engine control section of the instruction register. If bit 5 is set, the MBISTRESULT[1] signal is asserted for a single cycle for each failed compare. If bit 5 is not set, the MBISTRESULT[1] signal is sticky, and is asserted from the first failure until the end of the test.

At the completion of the test, the MBISTRESULT[2] signal goes HIGH. The MBISTRESULT[0] signal indicates that an address expire has occurred and enables you to measure sequential progress through the test algorithms.

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